In some countries some parts of history books of students have been removed by authorities of the time. For example, it has happened for Achaemenid Empire (a part of ancient Iran history) 2 years ago in history books of Iranian students. It is a kind of ideological censorship but I am finding for a better term or word to describe it.

Iranian authorities justified it as an attempt to focus on the Islamic part of Iran history and avoid of reading something complicated which may not be according to Islamic culture of Iran nowadays.

However, Iranians think there is nothing offensive and criminal in those ages but it has been removed because talks about a different religion, handwriting, and culture that Iranians had and caused golden ages for Iran history without Islamization. It is ironically strange because the other authorities remove dark histories like criminal attacks and genocides but Iranian authorities removed the most glorious part of Iran history! I think we have to find or create a new word to describe it if there is nothing similar!

Censoring is too broad and general. The word or phrase should not be one that is used for censoring sexual or offensive materials from art or literature, or removing something which seems vulgar or offensive. Historical revisionism might be the correct kind of word, but it refers to Communism ideas about revision about the history, religion, and political ideas, so it may be a correct word for North Korea but not about Iranian kind of it.

Maybe "expurgation"? Webster's says that "expurgate" means "to cleanse something morally harmful, offensive, or erroneous; esp to expunge objectionable parts before publication or presentation." Of course, "objectionable" is very often in the eyes of the censor. The root word here is the same as for "purge."
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Sven YargsApr 26 '13 at 0:54

@SvenYargs It is applied for censoring sexual or offensive materials from art or literature.
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Persian CatApr 26 '13 at 1:30

a.k.a. "revisionist history." @Persian: Even though those terms can be applied to historical and political ideas and Communist countries, the term has a much wider use than that. Read more.
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J.R.Apr 26 '13 at 2:04

If historical revisionism is not immediately negative enough, then the adjective Orwellian can be added or used. Generally, this conjures the notion of the Ministry of Truth's wholesale reworking of history depicted in 1984; however there is at least one analysis of Orwell/Blair's own politics which identifies him as revisionist (and particularly as a Holocaust denier), so the word has a double impact.

During the Second World War, George Orwell wrote a weekly radio political commentary, designed to counter German and Japanese propaganda in India, that was broadcast over the BBC overseas service. His wartime work for the BBC was a major inspiration for his monumental novel, 1984. Very few readers of 1984 know, for example, that Orwell's attack against the perverse double-talk language called Newspeak was based on the author's revulsion against Basic English, an artificial language that Churchill's wartime cabinet wanted the BBC to use in its overseas propaganda. Similarly, Orwell's model for the lying Ministry of Truth was the British wartime Ministry of Information, which censored BBC broadcasts. The shorthand form, Minitrue, was taken directly from the Ministry of Information telegraphic address, Miniform.

Throughout his lifetime, the great English writer continually questioned all "official" or "accepted" versions of history. As early as 1945, just after the end of the war in Europe, he expressed doubts about the widespread stories of "gas oven" exterminations (Notes on Nationalism). George Orwell was a revisionist. He detested officially sanctioned atrocity and hate propaganda. If he were alive today he would certainly be nauseated by the pervasive Holocaust propaganda of our times. And as a staunch lifelong supporter of free speech and open historical inquiry, he would undoubtedly defend the right of revisionist historians to present their challenging views to the world.

@Persian: Sure, it can be the answer. Read your question again: "In some countries some parts of history books of students have been removed by authorities of the time." But why did the authorities remove it? If it's because they found the content "offensive" (mind you, offensive is a very broad word), then this term could be applied. It may not be the word you're looking for, but it's still a valid answer to the question.
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J.R.Apr 26 '13 at 2:27

Revisionism is probably the best, but the verb revise is a neutral term. A common negative verb is whitewashing, which is purposely distorting or hiding the facts (often historical) to make something appear more favorable.